Blown microfiber webs having a novel pillowed structure, and a novel method for making such webs, are described in a U.S. patent application of Humlicek, Ser. No. 507879, filed Sept. 20, 1974 (the same day as the present application). Conventionally, "blown microfibers" -- which are discrete, very fine, discontinuous fibers prepared by extruding liquified fiber-forming material through fine orifices in a die into a high-velocity gaseous stream, where the extruded material is first attenuated and then solidifies as a mass of the fibers -- are collected on a small-mesh collection screen that is moved transversely through the gaseous stream. A flat, or constant-thickness, coherent web is produced that is most often used in its collected form after being cut to useful sizes.
Humlicek discovered a radically different pillowed structure that can be made by making special use of perforations in the collection screen. He found that microfibers could be blown at the screen so as to cause them to penetrate into the perforations, while still closing and continuously bridging over the openings. At the land areas of the collection screen, the microfibers become compacted; but at the openings, low-density pillows of microfibers are formed.
The resulting microfiber web has a number of important advantages. For example, the pillowed low-density regions may be made with such a low density that the overall density of the web is lower than the density of previous blown-microfiber webs of comparable tensile strength. At the same time, the internal volume and the exterior surface area of the web are increased. These features are of special significance for use of the web in sorption, filtering, insulation, and like purposes.
However, the novel pillowed blown-microfiber webs still have a recognized disadvantage of blown microfiber webs. Because the webs consist of discontinuous fibers, and because blown microfibers do not generally have the strength of some synthetic fibers, the web has less tensile strength than is desired for many purposes. For example, one major use of microfiber webs is to sorb oil spills from bodies of water, and the higher the tensile strength, the greater the handleability of the web. Further, it is often desired to expel collected oil from an oil sorbent web and reuse the web, which subjects the web to further destructive stresses. Improvement in the tensile strength and integrity of blown microfiber webs would increase their utility in oil sorption, and would in general make possible a fuller realization of the potential of such webs.